1. Field of the Invention
The present invention relates generally to methods and apparatus to schedule and wirelessly transmit information packets and more specifically to employ superposition coding to improve the forward link data throughput performance in a wireless communication system.
2. Background
There are a variety of wireless communication standards that may control the communication in a cellular communication system. The cdma2000 1xEV-DO standard (“cdma2000 High Rate Packet Data Air Interface Specification,” TIA/EIA/IS-856) is a system for packet data communication developed by Qualcomm Inc., U.S.A. in the late 1990's to provide general data communication services in a wireless mobile environment. The 1xEV-DO system adopts intrinsic resource assignment methods corresponding to the characteristics of forward and reverse links.
Under the 1xEV-DO standard, the base station may transmit only one data packet to one cell phone during that moment in time. To determine which of the thirty cell phones in the example above may receive their data packet during a particular moment in time, the base station may utilize a pilot signal. In operation, a base station may continuously transmit pilot signals with a constant power. On receiving a pilot signal, a cell phone determines the intensity of the received pilot signal and sends the results back to the base station in the form of a requested Data Rate Control (DRC).
Fading is the probabilistic variation in the received intensity of a radio transmission. The phone's distance from the base station may affect the received pilot signal intensity. Also, dynamic events, such a truck passing between the cell phone and base station, the pilot signal reflecting off buildings to combine with or cancel the main pilot signal, may affect the received pilot signal intensity. In short, distance and interference conditions create disparity in this Forward Link Signal-to-Interference-and-Noise Ratio (FL SINR) and thus affect the requested DRC of each phone.
At the base station, a scheduler algorithm may rank each cell phone by its pilot signal intensity (namely, requested DRC) and utilize that ranking to determine which one cell phone may receive the next data packet. In some cases, a strongest cell phone's pilot signal intensity may be as much as 20 decibels (dBs) less than the next candidate ranked pilot signal intensity. In a typical intrinsic resource assignment method, the base station may send out that data packet which corresponds to the cell phone having the “most” deserving SINR. During that moment in time, the most deserving user's needs may be addressed while the needs of the remaining users (in the above example, the needs of twenty-nine users) may have to wait.
Conventional intrinsic resource assignment methods attempt to provide fair service to all cell phones. This leads to a problem in that the most deserving user limits the overall system data throughput performance. Moreover, users with FL SINRs that are higher than the FL SINR of the most deserving user are penalized with a lower than potential throughput and higher delays for their particular cell phone. Even though the most deserving user is given preference over many other users, it may be important to continue to meet the needs of the most deserving user. There is therefore a need in the art for a system that improves the forward link data throughput performance and diminishes the delays for users with FL SINRs that are higher than the FL SINR of the most deserving user while meeting the needs of the most deserving user.